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Abstract  

Headspace analysis by means of sensor arrays has been successfully applied to a wide range of qualitative applications. In this study, a six element array of coated Quartz Crystal Microbalance (QCM) sensors was used for the headspace analysis of milk volatiles. The sensors were exposed to uncontaminated samples of milk and samples contaminated with Pseudomonas fragi (Ps. fragi) or Escherichia coli (E. coli). Principal component analysis (PCA) was used to analyse the sensor array responses. No discrimination between uncontaminated milk samples and those contaminated with Ps. fragi was observed. This can be explained by Ps. fragi being a poor fermenter of milk. However, encouraging results were found for the discrimination between the milk samples and those contaminated with E. coli.

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Abstract  

The extraction of Co2+ from a 0.1M ionic strength acetate buffer by acetylacetone, and a mixture of acetylacetone and pyridine or triethylamine was investigated at various temperatures. The enthalpy and entropy change data for the synergistic extraction support a model in which the Co2+ ion in the acetylacetonate complex expands its coordination number from four to six in order to accomodate the two N-base molecules. The steric hindrance caused by triethylamine is also reflected in the thermodynamic data.

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Abstract  

Quartz crystal microbalances have high mass sensitivities. Their application in gas sensing has been limited because they are required to have both high selectivity and reversibility. Yet by the inherent nature of their operation these properties are mutually exclusive. One approach to this problem is to use an array of quartz crystal microbalances. We have used an array of six coated quartz crystal microbalances for the classification of methanol, propan-1-ol, butan-1-ol, hexane, heptane and toluene. A novel classification scheme using fuzzy membership functions was found to be highly efficient.

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Three accurate, sensitive, simple, and precise spectrophotometric methods along with thin-layer chromatography (TLC)–densitometric method were developed, optimized, and validated for the determination of folic acid in the presence of its two impurities (photodegradation products), namely, pteroic acid and para-aminobenzoic acid. Method A is the ratio difference spectrophotometric method (RDSM) which depends on measuring the difference value in the ratio spectrum, where the difference between 291 and 313 nm was used for the determination of folic acid, while the difference between 305 and 319 nm was selected for the estimation of para-aminobenzoic acid; on the other hand, pteroic acid can be determined using the first derivative of ratio spectra spectrophotometric method at 262 nm. Method B is the double-divisor spectrophotometric method (DDSM); this method is based on using the ratio spectrum obtained by the division of the spectrum of ternary mixture by the spectrum of binary mixture containing two of the three mentioned components, and in this method, folic acid, para-aminobenzoic acid, and pteroic acid were measured at 242, 313, and 258 nm, respectively. Method C is the mean-centering of ratio spectra spectrophotometric method (MCR); in this method, folic acid, para-aminobenzoic acid, and pteroic acid can be measured using the mean-centered second ratio spectra amplitudes at 317–318 (peak to peak), 264–265 (peak to peak), and 232 nm, respectively. Lastly, method D is a TLC‒densitometric one that depends on the separation and quantification of the mentioned components on TLC silica gel 60 F254 plates, using methanol‒ iso-propanol‒water‒acetic acid (9:0.5:0.5:0.2, by volume) as the developing system, followed by densitometric measurement of the separated bands at 280 nm. Method validation was carried N.W. Alia, N.S. Abdelwahaba, M.M. Abdelrahmana, and S.I. Tohamy, Pharmaceutical Analytical Chemistry Department, Faculty of Pharmacy, Beni-Suef University, Alshaheed Shehata Ahmed Higazy St., 62514, Beni-Suef, Egypt; and B.A. El-Zeiny, Pharmaceutical Analytical Chemistry Department, Faculty of Pharmacy, Cairo University, Kasr EL-Aini Street, ET 11562, Cairo, Egypt. *E-mail: salwatohamy2015@yahoo.com out according to the International Conference on Harmonisation (ICH) guidelines, and the proposed methods were successfully applied to the analysis of folic acid in pharmaceutical formulations, where no interference from additives has been found. The results obtained by the proposed methods were statistically compared with those obtained by the official reversed-phase high-performance liquid chromatography (RP-HPLC) method, in which no significant difference was observed.

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Abstract

A series of CoMo/γ-Al2O3 catalysts was prepared with [Co/(Co + Mo)] ratios of 0.3, 0.4 and 0.5 while maintaining a total metal content of 19 wt%. These catalysts were tested in a batch autoclave reactor after presulfiding with the objective of studying the influence of Co/(Co + Mo) ratio on the hydrodesulfurization (HDS) pathways of benzothiophene (BT) and dibenzothiophene (DBT). The results of this study have clearly demonstrated that the Co/Co + Mo ratio has a significant influence on the overall HDS of BT and DBT as well on the direct desulfurization (DDS) pathway, but showed no influence on the hydrogenation pathway. A Co/Co + Mo ratio of 0.4 was found to be optimum for both overall HDS as well as the HDS by DDS pathway.

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Abstract  

An electronic nose utilising an array of six-bulk acoustic wave polymer coated Piezoelectric Quartz (PZQ) sensors has been developed. The nose was presented with 346 samples of fresh edible oil headspace volatiles, generated at 45°C. Extra virgin olive (EVO), Non-virgin olive oil (OI) and Sunflower oil (SFO), were used over a period of 30 days. The sensor responses were then analysed producing an architecture for the Radial Basis Function Artificial Neural Network (RBF). It was found that the RBF results were excellent, giving classifications of above 99% for the vegetable oil test samples.

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Abstract  

The effect of different relative humidity (RH) on the response of a six-polymer coated Quartz Crystal Microbalance (QCM) sensor based electronic nose (EN) was investigated, RH 30 and 50% respectively. Increases in the sensor responses were observed for an increase in RH. A stainless steel pre-concentration tube (PCT) containing Porapak-S and a nichrome heating element was developed to minimise the effect and allow for chromatographic pre-separation. Breakthrough times of chemical compounds through the PCT were experimentally determined and used to select a mixture of water and toluene as a suitable sample for pre-separation. The PCT was capable of separating the water from the toluene and the EN was competent at evaluating the concentration of toluene in the solution.

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Summary

Ashwaghanda, Withania somnifera, is one of the most widely used herbs in Ayurvedic medicine. Leaves and roots are the traditionally used parts of the plant. An RP-HPLC method using a binary acetonitrile-water gradient containing 0.1% acetic acid has been developed for analysis of withaferin A. The method was validated in accordance with ICH guidelines and used for analysis of the withanolide content of the flowers, leaves, and roots of W. somnifera. The withanolide content was highest in the flowers.

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Summary

Three simple, sensitive, and validated methods were developed for the quantitative determination of fosinopril sodium (FOS) and hydrochlorothiazide (HCZ) in the presence of an HCZ impurity, chlorothiazide (CZ). The first method (I) was the ratio difference spectrophotometric method (RD), in which a standard spectrum of 8 µg mL−1 HCZ was used as a divisor, and the difference in amplitude values at 204.6 and 231.2 nm and 290 and 302.6 nm was used for the determination of FOS and CZ, respectively. Meanwhile, for the determination of HCZ, a standard spectrum of 6 µg mL−1 CZ was the chosen divisor, and the amplitude difference at 275 nm and 293.6 nm was selected for the calculation of its concentrations. The second method (II) was mean centering of ratio spectra spectro-photometric method (MCR), which depended on the implementation of the mean-centered ratio spectra in two successive steps and the measurement of the amplitudes of the mean-centered second ratio spectra at 243.4 nm for CZ and peak-to-peak amplitudes at 215.6 and 215.8 nm for FOS and at 223.8 and 224 nm for HCZ. On the other hand, the third method (III) was thin-layer chromatography (TLC)-densitometry at which the chromatographic separation of this ternary mixture was performed using pre-activated silica gel 60 F254 TLC plates and a developing system mixture consisting of ethyl acetate-chloroform-methanol-formic acid (60:40:5:0.5, by volume) with ultraviolet (UV) scanning at 215 nm. The developed methods were validated according to the International Conference of Harmonization (ICH) guidelines and were successfully used for the determination of FOS and HCZ in their pharmaceutical formulations. Also, a statistical comparison between the developed methods and the reported HPLC method was attained. Using Student's t-test and F-test, the results confirmed that there was not any significant difference between them regarding accuracy and precision.

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